Electrocochleography Dr Supreet Singh Nayyar AFMC For more

Electrocochleography Dr. Supreet Singh Nayyar, AFMC For more presentations, visit www. nayyar. ENT. com 22 -07 -2012

Headings � Introduction � Principles � Recording techniques � Interpretation � Clinical applications www. nayyar. ENT. com 22 -07 -2012

Introduction � Electrocochleography (ECoch. G) �Method for recording the electrical potentials of the cochlea �Stimulus-related �Often includes measurement of the whole nerve or compound action potential (AP) of the auditory nerve. www. nayyar. ENT. com 22 -07 -2012

Principles CM • An alternating current voltage that mirrors the waveform of the acoustic stimulus at low-moderate levels of stimulation • Generated predominantly by the outer hair cells • Phase and duration are stimulus dependent www. nayyar. ENT. com 22 -07 -2012

Principles � SP �A Direct Current generated predominantly by the outer hair cells �Seen as a DC shift in the CM baseline �Duration is dependent on the duration of the acoustic stimulus �Independent of stimulus phase www. nayyar. ENT. com 22 -07 -2012

Principles � AP � AC potential that represents the summed response of the synchronous firing of several thousand auditory nerve fibers � N 1 and N 2 are virtually the same components as waves I and II of the ABR � Independent of stimulus phase and duration. www. nayyar. ENT. com 22 -07 -2012

Principles � The normal SP duration is b/w 0. 30 and 0. 45 ms, and the absolute amplitude of the SP can range from 0. 1 m. V to 1. 0 m. V � AP has a latency of 1. 5 ms(1. 3 ms to 1. 7 ms) duration is normally between 0. 80 ms and 1. 25 ms, absolute amplitude can vary greatly, ranging from 0. 6 m. V to 3. 0 m. V www. nayyar. ENT. com 22 -07 -2012

Principles � Normal SP/AP ratios generally range from 0. 1 to 0. 4 across subjects with a mean value of 0. 25. � Graphic Angle Measurement (GAM) Technique www. nayyar. ENT. com 22 -07 -2012

Recording techniques � There are two, general approaches for recording ECoch. G �Transtympanic (TT) �Extratympanic (ET) www. nayyar. ENT. com 22 -07 -2012

Recording techniques � Recording parameters www. nayyar. ENT. com 22 -07 -2012

Recording techniques • The following suggestions are offered to help to reduce stimulus artifact ▫ test subjects in sound booth with the examiner and AEP unit ▫ ▫ located outside of the booth; the windows of the booth should be shielded with a copper screen; plug the AEP unit into an isolated electrical socket equipped with a true-earth ground; use a grounded cable for the primary electrode (such cables are commercially available); turn off lights in the testing room and unplug unnecessary electronic equipment (it also may be necessary to turn off the lights in the examiner room); consider encasing the transducer in grounded Mu metal shielding. www. nayyar. ENT. com 22 -07 -2012

Interpretation � Normal electrocochleogram from the tympanic membrane to clicks presented in alternating polarity at 80 d. B HL www. nayyar. ENT. com 22 -07 -2012

Interpretation � Normal electrocochleogram from the tympanic membrane to a 2, 000 Hz toneburst presented in alternating polarity at 80 d. B HL www. nayyar. ENT. com 22 -07 -2012

Clinical applications � Menieres’ disease/ Endolymphatic hydro � The reported incidence of an enlarged SP and SP/AP amplitude ratio in the general Meniere’s population is only approximately 60%-65% www. nayyar. ENT. com 22 -07 -2012

Clinical applications � Enhancement of wave I � Wave I is absent in the conventional ABR tracings but recordable with the ECoch. G www. nayyar. ENT. com 22 -07 -2012

Clinical applications � Intraoperative monitoring of inner ear and auditory nerve status during surgeries � identification of anatomic landmarks (such as the endolymphatic sac) www. nayyar. ENT. com 22 -07 -2012

Clinical applications � Other applications �Estimation of hearing thresholds www. nayyar. ENT. com 22 -07 -2012

Thank you For more presentations, kindly visit www. nayyar. ENT. com 22 -07 -2012